(1) Field of the Invention
This invention relates to an electrical insulating oil which comprises an improved recovered fraction.
More particularly, the invention relates to an electrical insulating oil comprising a by-product oil fraction having excellent low temperature characteristics, which fraction is prepared by bringing a by-product oil fraction into contact with alkylbenzenes in the presence of ZSM-5 type synthetic zeolite catalyst.
(2) Description of Prior Art
It has been industrially put to practice to alkylate benzene with ethylene in the presence of an alkylation catalyst so as to produce ethylbenzene. The obtained ethylbenzene is then dehydrogenated into styrene, which is widely used as a raw material for producing polystyrene and other chemical substances.
When ethylbenzene is produced, a heavier oil fraction containing diarylalkanes is formed by side reaction. For example, it is disclosed in U.S. Pat. No. 4,111,824 that the heavier oil fraction which is obtained by using aluminum chloride as an alkylation catalyst, can be used as an electrical insulating oil. The the heavier oil fraction contains diarylalkanes typically exemplified by diphenylmethane and 1,1-diphenylethane. Because these diarylalkanes have high aromaticity, the fraction is in itself desirable as an electrical insulating oil, especially for the use as a capacitor oil.
Nevertheless, because the freezing point of diphenylmethane among them is high, it is not suitable for the use as electrical insulating oil when good low temperature characteristics are required. However, even when 1,1-diphenylethane itself is recovered singly, it is not always suitable either for the use in the field of electrical insulating oil in which low temperature characteristics are required.
In addition, when diphenylmethane and 1,1-diphenylethane are recovered by separating them through distillation, rectifying towers having considerably large theoretical number of plates are necessary.
Therefore, in the case that desirable components as electrical insulating oils, especially those being advantageous in low temperature characteristics, are recovered from the above by-product oil fraction, even if the undesirable diphenylmethane could be removed by the difficult operation of distillation, it is difficult to recover an electrical insulating oil having good low temperature characteristics.